The nano Rectenna Project Design and Applications of UWB ...
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The nano Rectenna Project
Design and Applications of UWB Nano-Antenna Arrays
Zeev Iluz, Yuval Yifat, Doron Bar-Lev, Michal Eitan, Yoni Kantarovsky, Yoav Blau, Yael Hanein, Koby Scheuer, and Amir Boag
School of Electrical EngineeringTel Aviv University, Tel Aviv 69978, Israel
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The nano Rectenna Project
Largest of the 7 universities in Israel with ~ 28000 students
Tel Aviv University
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The nano Rectenna Project
Why Nanoantennas?
Field localization• Breaks the diffraction
limit (10-50nm resolution) - Imaging
• Smaller photodetectors (less dark current, faster response) - Detection
• Increasing resolution - information processing
Field enhancement• Up to 40dB power
enhancement• Increased
effective absorption cross section
• Enhancing nonlinear optics
Field detection• Phase
sensitive detectors
Design flexibility• Wavelength
scaling* – Hybrid detectors
• Load dependence response –sensing, active antennas
Coupling from near to far field• Efficient
surface phenomena detection
* P. Bharadwaj, B. Deutsch & L. Novotny, "Optical Antennas", Adv. Opt. Photon. 1, 438-483 (2009).
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Plasmonics and nano-antenna projects
Broadband antennas
Nonlinear optics
Particle trapping
D A E B F G
HolographySensors
Rectennas
The nano Rectenna Project
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UWB Antennas and Rectennas• Motivation• Rectenna concept• Dual-Vivaldi design• Fabrication• Performance evaluation• Rectifying devices• Conclusion and
Applications
The nano Rectenna Project
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Contemporary and Future World Energy Consumption 1990-2035*
Contemporary and Future World Energy Consumption By Fuel*
*The US Energy Information Administration (EIA) website
Qua
drill
ion
BTU
Qua
drill
ion
BTU
• Technology = Power
• Primary energy resources lead to pollution (e.g. global warming)• Possible solution – Renewable energy, particularly solar energy
Motivation for Solar Energy Harvesting
The nano Rectenna Project
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• The energy from 1hr of sunlight striking the earth ( ) ~ 1 year of consumed energy worldwide ( in 2001*)
• Two main commercial technologies:• Concentrating solar power (CSP) systems• Photovoltaics (PV)
Both technologies at present have low efficiency !
Wednesday,
Nano Rectifying Antennas f S l E H ti
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J20103.4 ⋅
J20101.4 ⋅
*The UN Development Program (2003) World Energy Assessment Report
A CSP System Typical Solar Cell
World insolation map
The nano Rectenna Project
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Any optical rectenna system will include:
1. Receiving antenna
2. Non linear load that rectifies the AC field
induced at antenna terminals3. In 1964, Raytheon demonstrateda helicopter powered by 2.45 GHzrectenna system.
The helicopter flew for over 10 hours
Alternative approach: optical rectenna system
The nano Rectenna Project
General Concept• NanoAntenna + high-frequency diode• EM radiation excites AC in nano-antenna• The high-frequency diode rectifies the AC
current• The outcome:
Detection + Second Harmonic Generation
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Guidelines for efficient rectenna1. Wideband (both impedance matching & radiation
efficiency)
2. Integrated antenna-to-waveguide device (matching
manipulations)
3. DC power lines that do not interact with antenna
operation (array configuration)
4. Metal’s skin depth
The nano Rectenna Project
The Skin Depth of Gold
Visible spectrum
• Skin depth ~ 13 nm in IR band
• Antenna thickness > 40-50 nm 12
The nano Rectenna Project
The Dual Vivaldi antenna geometry
zx
( )end end,x z
( )start start,x z
1 25 nmW =
250 nmL =
2 500 nmW =
• Classical Vivaldi - slot antenna with exponential taper • UWB impedance matching• End-fire radiation• Our approach: two end-fire Vivaldi antennas, placed opposite to one another• Peak gain at the antenna broadside direction. 13
The nano Rectenna Project
Both parallel plate waveguide gaps were excited coherently and in phase, using ports across the gaps:
Port 1Port 2
The parallel plate impedance ~ 0 1 / 78.5 ,Z W hη= = Ω 377η = Ω14
The nano Rectenna Project
Array configuration for Power harvestingSeries DC connection – no need for DC interconnects
Slight tuning of Design Parameters
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The nano Rectenna Project
Dual Vivaldi Antenna: Simulation results
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The return loss > 9.5 dB between (129% impedance bandwidth).
0.7 3.25μm−
The nano Rectenna Project
How does it work ?
17Benefits of coupling for wideband operation !
The nano Rectenna Project
The Dual Vivaldi input resistance and reactance
Multi resonance behavior - finite size traveling wave configuration
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The nano Rectenna Project
y-xy-z
Non symmetric far-field pattern due to the Quartz substrate
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Antenna configuration
Far-field directivity patterns in the y-x (vertical) and y-z (horizontal) planes
The nano Rectenna Project
The Dual Vivaldi radiation efficiency
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The radiation efficiency remains higher than 85% between (122% efficiency bandwidth).0.78 3.23μm−
The nano Rectenna Project
Visible Range AntennasAluminum Wideband
Efficiency 60-70 %
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The Fabrication Process
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The antennas structure, composed of a 7 nm adhesion
promotion layer of Cr followed by 33 nm of Au, was
patterned using E-beam lithography.
Both Open and Short circuits were fabricated.
The nano Rectenna Project
Fabrication Results
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W
H
c
g
SINGLE ANTENNA SPECIFICATIONAnt MeasuredAnt Design596580W[nm]471470H[nm]3125g [nm]5040c[nm]
ARRAY SPECIFICATION1.791.79dx[um]
0.470.47dy[um]
The nano Rectenna Project
Array Fabrication
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Open Circuit Short Circuit
The nano Rectenna Project
The Reflection Measurement Setup
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The nano Rectenna Project
Design Verification
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How to measure impedance of Nano-Antennas?
How to measure impedance of Nano-Loads?
Coupling Antennas to Loads
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An infinite antenna array unit cell, as a loaded scatterer:
212, ( , ) 2, (0,0)
2,11
22 22
22 22
12 21 12
21 12 2 (01 ,0)2,
CBA
, ) 1( 2+
1hL hh hv
vh v
hTE m n TE
TM
h v
v h v vn vLTM m
S S S SS S S SS
aab
S SS S
b
Γ
= ⋅
− Γ
The incident, scattered, and reradiated waves can be related by S-parameters’ network equations:
A load influence B Tx. & Rx. characteristics
C structural scattering
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open short load2, ( , ) 2, ( , )2, ( , )
11 open short2, ( , )2, ( , )
2TE m n TE m nTE m n
TE m nTE m n
b b bS
b b
+ − ×=
−
( )open load2, ( , ) 2, ( , )
21 12 112, (0,0) 2, (0,0)
1TE m n TE m nh h
TE TE
b bS S S
a a
= − −
Illuminating the array with a single mode and using 3 different loads (“open”, “short” and matched load) we determine antenna parameters:
Unknown load reflection coefficient measurement:
( )unknown load2,TE( , ) 2, ( , )
unknown open load unknown open2, ( , ) 2, ( , ) 11 2,TE( , ) 2, ( , )
m n TE m n
TE m n TE m n m n TE m n
b b
b b S b b
−Γ =
− + −
The nano Rectenna Project
The S-parameters Measurement Setup in RF
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The maximum error in the return loss is 3%, which is less than the resistor manufacturing tolerances (5%).
RF Direct (simulation) vs. Scattered (measurements)
The nano Rectenna Project
RF measurements for unknown load (R=2 KΩ)
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Typical error of 9% and a flat response vs. frequency, as expected
The nano Rectenna Project
High Frequency Diodes
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The nano Rectenna Project
CNT diodes
A single CNT connecting Ti electrode (Schottky) with Pt electrode (Ohmic) on a Quartz substrate.
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The nano Rectenna Project
CNT diodes model
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Carbon nanotubes
The nano Rectenna Project
Dual Vivaldi + MIM
Au
Al
nm isolation layer Al
Aunm isolation
layer
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The nano Rectenna Project
Main Achievements• Arrays of regular and nano-gapped nano antennas (using E-beam
lithography)• Full antenna model was constructed and various antennas were
simulated• Comparison between simulation and experimental data (good
correspondence• Dual-Vivaldi UWB antennas• High efficiency validated (both numerically and experimentally)• CNT & MIM diodes were fabricated and successfully realized
including electrical characterization. Novel methods suited for high resolution patterning of these structures were developed
• CNT & MIM diodes are studied
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The nano Rectenna Project
Additional Applications Particle Trapping and
Sensing
Refractive Index Sensing
Reflectarrays
Second and Higher Harmonic Generation
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The nano Rectenna Project
Trapping and sensing nano-objects using nano-antennas
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Sensors: trapping and identify nano-particles
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Sensors: trap and identify nano-particles
The nano Rectenna Project
Trapping with DEP
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• Dielectric particles manipulated through high-gradient electric fields
• Force depends on:– Particle Geometry– Dielectric properties of
particle– Dielectric properties of
medium
( )( )
( ) ( )
Re ( ) ( )DEP
m f
t t
K t tε
= ⋅∇ =
= Γ ⋅∇
F μ E
E E
2p m
fp m
Kε ε
ε ε−
=+
3sphere 4 RπΓ =
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Optical DEP – numerical simulation• E-field distribution
calculation performed with CST
• Motion equations found from DEP force:
• MC motion simulations performed
DEP randdm fdt
= + −v F F v
DEP force
Random motion
Friction (medium and
geometry dependent)
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DEP Experimental setup• Trapping setup is
added on characterization setup
• Sample is placed at bottom of basin
• Chip illuminated with high power source (Pin=1W)
A B
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Preliminary results
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Detection concept - summary• Antenna array placed
under particle colloid• Array illuminated• DEP trapping occurs• Resonance change in
antenna• Scattering properties
modified• Detection through
optical scattering
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Refractive Index Sensor concept
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Wood’s anomalyThe impinging beam excites a surface wave on the surface.Accompanied by strong variations in the amplitudes of the Bragg diffraction lobes.
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Splitting Mechanism
xdiff Gmk
±=
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Theory vs. ExperimentsFOM and sensitivity depends on incident angle and surrounding RI.
∆λFWHM
𝑆𝑆 =𝑑𝑑𝜆𝜆𝑑𝑑𝑑𝑑
𝐹𝐹𝐹𝐹𝐹𝐹 =𝑆𝑆
Δ𝜆𝜆𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹
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Theory vs. Experiments
n=1.36 n=1.404
Tilting the impinging beam by ~0.5º yields a narrow peak.Sensitivity of S>1000RIU and FOM~150-210
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Phased reflectarraysInduce an arbitrary phase profile using nano-antennas.Conceptually similar to SLMs but with sub-wavelength resolution.The challenge: Design a set of antennas covering 2π phase shiftwith low sensitivity to fabrication tolerances.Our solution: Employ coupled dipole-patch antennas.
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Beam-Shaping: The unit-cellThe combination of dipole and patch antennas provides multiple multi-curve phase response.Modifying the dipole length and patch width allows for tuning the phase response.
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Beam-Shaping: deflect-array fabrication
A B C
A B C
D A E B F G
D A E B F G
20° deflection45° deflection
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Nano-Antenna reflection holographyDesign a phase reflector which generates an arbitrary beam shape.High efficiency & resilience to fabrication errors.
The nano Rectenna Project
AlgorithmA
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Hologram Efficiency
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Nano-imprinting lithography (NIL)• Avoid expensive E-beam lithography
• Single master can be reused indefinitely
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High Harmonic Generation
Tightly focus light on a nonlinear materialGeneration of higher harmonics.Re-emit the higher harmonics.No need for phase matching, etc.
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Maximizing SHG
Pump and Polarization effects-numerical results:(a) FH field distribution for propagation from the
LiNbO3 or the Air;(b) The LiNbO3 effect on the field enhancement in
recessed and on-top Bowtie nanoantennas.
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Experimental setup FH source is a femtosecond fiber mode locked laser.
λ=1550 nm, pulse duration: 150 fs, repetition rate: 80 MHz Beam is linearly polarized and its power is monitored
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Experimental results Generation of SH signal observed experimentally The intensity of the SH signal scales as the square
of the intensity of the FH power. Thisis a clear sign of SHG.
SH signal depends strongly onpolarization of the FH pump.This is a clear indication ofthe importance of the nano antennas in the process.
Conversion efficiency is notyet determined as collection efficiency is unknown.
0 5 10 15 20 250
500
1000
1500
FH [mW]
SH [p
W]
FH z-polarizedz polarized Quadratic FITFH y-polarizedy polarized Quadratic FIT
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SummaryNano-antennas may provide an inexpensive, efficient and simple solution for various nano-photonics applications.
Nano-Rectennas for power harvesting and detection fabricated and characterized.
Beam deflection and wide-angle holography using nano-antennas demonstrated with efficiencies exceeding 50%.
High sensitivity slot-antenna based RI sensor with record high sensitivities and FOM demonstrated.
Rapid optical sensing possible through trapping with nano-antennas
Nano-antennas can facilitate efficient HHG on surfaces.
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